Loud speaker having balanced magnetic circuits



' M y 0 1933 T. A. HUNTER Er AL 1,912,073

LOUD SPEAKER HAVING BALANCED MAGNETIC CIRCUITS Filed Jan. 26, 1931 4 Sheets-Sheet 1 IINVENTOR.

C'ofi/ai/vr ll/161010 W a I v A TTORNEYS May 30, 1933. T. A. HUNTER ET AL ,91

LQUD'SPEAKER'HAVING BALANCED MAGNETIC CIRCUITS Filed Jan. 26, 1931 4 Sheets-Sheet Q'IINVENTOR; flowztd J W dmmdzzw A TTORNEYS y 30, 1933- T. A. HUNTER ET AL 1,912,078

LOUD SPEAKER HAVING BALANCED MAGNETIC CIRCUITS j ./Z L 40 I INVENTOR.

1mm @fiww y el- ROM ATTORNEY? May 30, 1933. T. A. HUNTER ET AL 1,912,078

LOUD SPEAKER HAVING BALANCED MAGNETIC CIRCUITS Filed Jan. 26, 1931 4 Sheets-Sheet 4 INVENTOR. By Wou'ald @1- Row A TTORNEYS Patented May 30, 1933 UNITED STATES PATENT OFFICE 'rnmnonn A. HUNTER AND RONALD J. ROCKWELL, OF CINCINNATI, OHIO, ASSIGNOBS TO THE CBDSLEY RPIO CORIORATION, 01' CINCINNATI, OHIO, A CORPORATION 01' OHIO LOUD SPEAKER HAVING BALANCED MAGNETIC CIRCUITS Application filled January 86, 1981. Serial No. 611,158.

Our invention relates to improved types of loud speaker motors, and w ile it is aplicable to motors in which the field fiux 1S furnished by a permanent magnet or ma etic system, the specific embodiment which we shall describe in making a disclosure of my invention, will be a type of motor in which the field is electro-magnetic.

When the principles of operation of our structure 'are made clear in the ensuing specification, it will be understood that our invention may be embodied in or employed in connection with, a wide variety of loud speaker constructions. The particular construction which we shall describe as enemplary, is a construction made by us in which the parts have been reduced to their simplest form, both from the operating standpoint and from the standpoint of cost.

It has been one of our jects to simplify the construction and decrease the cost of loud speaker motors, and we have succeeded in constructing a motor in accordance with the following disclosure at a commercial cost materially beneath the cost of any other commercial loud s eaker of which we are aware. As distinguis ed from the operative elements of our speaker, certain constructional features of the exemplary commercial embodiment which we shall describe herein are the invention of Ralph H. Langley, and are claimed in his 00- nding application Serial No. 509,555, filed gin. 19, 1931. Fundamentally our invention is addressed, however, to a new principle of loud speaker operation which will be fully explained, and which enables us to construct magnetic re roducers having enhanced efiiciency, being rec from a number of the well known difliculties hitherto attendant upon speakers of the magnetic armature type, and having substan tially all of the advantages hitherto obtained in the popular moving coil type, of loud speakers.

The objects of our invention will be set forth in detail hereinafter, or will be entirely apparent to one skilled in the art upon reading these specifications, and reference is now made to the drawings in which Figure l is a diagrammatic perspective representation of the parts of the speaker embodying our invention;

Figure 2 is also a dia ammatic representation showing the re ationship of the armature and the magnetic bridge portions to the poles of my field structure;

Figure 3 is a diagram in which magnetic flux 1s approac tion;

Figure 4 is a scale drawing showing in plan one of the laminations of a field element;

Figure.5 is an edgewise view of an assembled field element;

Figure 6 is an elevation thereof;

Figure 7 is a plan view of one of the supporting brackets;

Figure 8 is a side elevation thereof;

Fi re 9 is an end elevation of the same brac et;

Figure 10 is a side elevation of an assembly of brackets and the field element of F1 ures 5 and 6;

igure 11 is an end elevation of thesame structure;

Figures 12, 13 and 14, are respectively side and end elevations and a top plan view of one of the elements forming the return magnetic path or magnetic bridge circuit of our apparatus;

Figure 15 is an end elevation; and

Figure 16 is a side elevation of one of the voice coil structures;

Figure 17 is a side elevation; and

Figure 18 is an end elevation of one of the spring retaining devices for the voice coils;

Figure 19 is an elevation of the armature and the attached driving rod";

Figure 20 is a plan view of the armature;

Figure 21 is an end elevation of a completed motor;

lotted against current to show the to a condition of magnetic satura- Figure 22 is a top plan view of a com- I pleted motor; I

Figure 23 is a sectional view of a motor taken along the lines 23-23 of Figure 22;

Figure 24-. is a side elevation of the completed motor; and

Figure 25 is a sectional view of the motor taken along thelines 25-25 of Figure 24.

One of the objects of our invention has been to produce in a magnetic armature type speaker, a construction in which a return path is provided for the alternating or fluctuating flux in the armature, which path is not co-extensive with the path of the flux and field structure. Accordingly, we have devised, as will fully be explained, a structure in which the return path for the armature flux is in a structure lying essentially in a plane transverse to the plane of the main field structure. As has been understood by investigators in this field, one of the disadvantages of the magnetic type of loud speaker has been the permeation of the field structure by the alternating flux produced in the armature.

Another well known disadvantage of the magnetic type speaker has been the saturation of the armature with the magnetic flux produced by the field, and it has been another object of our invention to produce a. magnetic type speaker in which the armature is practically free of magnetic saturation due to the field.

Due in part to the foregoing disadvantage, viz., the saturation of the armature by the field flux, but also affected by other factors, the armature of magnetic type speakers has been less readily'able to give satisfactory reproduction of impressed signals because it is in a state of relative unbalance upon movement; that is to say, the closer the armature approacheseither pole of the field. the more strongly it is attracted to the said pole. and so great is the increase in this attraction upon movement that the motion-response to the variations in the armature actuation current is no longer true. The response of such a motor is essentially non-rectilinear; and it is an object of our invention to produce, and we have succeeded in producing, a motor the response of which is much more nearly rectilinear.

The essential features of our motor are set forth diagrammatically in Figure 1, wherein we have shown a field structure comprising a core of essentially C shape, and having a back portion 1, side portions or legs 2 and 3, and opposite portions on the opposite ends of these legs which are essentially pole pieces, and may conveniently be called N and S since they will be referred to in this way in Figure 2 in connection with an explanation of the operation of our motor. The pole pieces N and S are separated by a space 4, which is an air-gap in which an armature 5 of strip form may move. It will be understood that this armature is mounted in suitable supports at its ends and is free to vibrate in its central portion,which is the portion located between the pole pieces N and S. A field coil 6 has been indicated diagrammatically as situated upon the back portion of my field core structure. \Vh'en this coil is energized b direct current, the

field core structure wil be ma etized and permeated by a constant flux. t may be so magnetized that the pole pieces marked N and S will be respectively the north and south poles of the magnetic structure, the flux across the air-gap 4 passing throu h the central portion of the armature 5. e have indicated diagrammatically voice coils 7 and 8 upon the portions of our armature 5 which extend beyond the air-gap. These coils are connected in series, but are wound in the opposite direction so as to have an opposite magnetic effect upon the central por tion of the armature. These coils are intended, of o0urse,'to be energized by a voice current of fluctuating or alternating character. The passage of this current in one direction will tend to magnetize the armature with a north pole at its center, while the passage of the current in the opposite direction will tend to magnetize the armature with a south pole at its center. A loud speaker motor constructed merely as just described would be operative, but its GfilClEIlcy would be relatively low because there would not be any closed magnetic circuit for the alternating flux set up in the armature. A feature of our construction is the provision of means for completing the magnetic circuit for the armature flux, and in the preferred embodiment illustrated in Figure 1, we have shown magnetic bridge arms or by-pass path constructions 9, 10, 11 and 12. These arms connect the pole pieces N and S with the outer ends respectively, of the armature. Their function will now be explained more in detail.

I have shown in Figure 2 the pole pieces N and S with the armature 5 lying in the air-gap 4 between them. The armature is connected by a suitable drive rod 13, passing through a perforation 14 in the pole iece N and connecting the armature either irectly or through a suitable motion transmitting or converting mechanism to a vibratile device, such as a cone 15. The magnetic arms 9 to 12 inclusive, are shown in elevation, and the voice coils have been indicated at 7a and 8a. When the field structure is actuated by a suitable direct current, there will be a flux in the pole pieces N and S and across the air-gap 4 in the direction of the arrows in Figure 2. The arms 9 to 12 are magnetic arms, and as respects the field flux, the. arms 9 and 10 upon the one side and the arms 12 and 11 upon the other act as magnetic by-pass paths for the field flux, and they will be saturated with a magnetic flux in the direction of the arrows. It is our desire to have them saturated as aforesaid, and for this reason they are made of relatively light magnetic material; They may be made of thick material, but the operation of our speaker will not be entirely the same as that which we shall presently describe; and although good speakers may be made this way, the relationship of parts is very much more exact and hard to obtain than if the paths are made relatively li ht and are kept substantially saturated. n Fi re 3 we have,

by way of example, plotted ux against current to produce a curve 16, showing the degree of magnetic saturation in one of our arms. \Ve have found it preferable so to proportion the size of our arms with relation to the size of the field structure and the flux therein, that the arms will be operated at some point high up on the saturation curve, such as the point 17. a

In considering the operation of our speaker, the arms 10 and 11 may be first'considered. If the coils 7a and 8a, are magnetized by a current which tends to produce a north pole at the center of the armature, the direction of the flux in the armature will be that of the small arrows within the ends thereof. A flux flowing inwardly in the left hand end of our armature must take as its return path, the pole piece S and thear'm 11. The arm 11 is saturated in the direction of the arrow, and therefore is a low reluctance path. Flux flowing inwardly in the right hand end of our armature must take a path embracing the arm 10 and the pole piece S. The arm 10 is saturated in the direction of the arrow; but the direction of the flux in the armature is opposite to this and therefore can flow in the arm 10 over a relatively low reluctance path opposite in direction to the direction of saturation therein. Thus a magnetic circuit for the armature flux is presented by the right hand end of the armature, the pole piece S and the arm 10. The central portion of the armature is more strongly magnetized as a north pole, and is repelled from the pole piece N and attra-ted to the pole piece S.

If there were in Figure 2 no arms 10 and 12, it is clear that the armature would be permeated and perhaps saturated by the ield flux, since there would be a magnetic circuit between the pole pieces N and S comprising in sequence, the arm 9, the armature, and the arm 11. A magnetic speaker of some, etliciency can be made in this way, and its operation is vastly improved over that which results when no return paths are provided for the armature flux. The situation which has been. described for one direction of the alternating voice coil current will, of course, be reversed for the other alternation; and if the direction of the current in the voice coils 7a and 8a tends to magnetize the,

11, and a low reluctance path comprising the arm 9.

Now, when there is, added to this system the arms 10 and 12 several results are accomplished. Since the arms 9 and 10 on the one side and tliearms 12 and 11 on the other .form magnetic by-pass paths for that portion of the field flux which they can carry up to their point of saturation, and since the armature is connected between these by-pass paths, there is produced a balanced magnetic bridge circuit, in which the armature is substantially unsaturated by the field flux, in which the production of an alternating flux in the armature is not modified by any substantial resident magnetic permeation in the armature, and in which magnetic circuit return paths for the alternating flux in. both ends of the armature are provided. It will be noted also, that the magnetic circuit or circuits for carrying the alternating flux of the armature are in a plane different from the plane of thefield core, and that there is substantially no tendency for the field core to carry the alternating flux produced in the armature.

Let it be supposed that the action of the coils 7a and 8a is to produce a north pole at the center of the armature 5 in Figure 2. In accordance with the foregoing explanation, it will be clear that there will be presented to this flux relatively high reluctance return paths comprisin'garms 9 and 12, and relatively low reluctance return paths comprising arms 10 and 11. Upon the passage of the current in the opposite direction, i. e. so as to magnetize the armature with a south pole at its center, the paths embracing the arms 9 and 12 will be low reluctance paths, and the paths embracing the arms 10 and 11 will be high reluctance paths. Since the flux flows in the low reluctance paths essentially by: bucking a saturation flux therein, it will be clear that our construction pro vides shifting balance points for our armature, lying out upon the several arms. The function of the return paths in strengthening the armature flux will be apparent, and the repulsive and attractive forces acting upon our armature at its central portion will, of course,'produce in it the vibrations which are transmitted by the drive rod 13 to the vibratile device 15 in reproducing sound. Our armature is substantially not permeated by the field flux, and itsresponse to fluc- I u i tuations of the armature current s not only true, but powerful. I

Hereinabove we have described our motor as operating with what we have termed a strip form' armature with either a pair of magnetic arms connecting the ends of our armature respectively with the )010 pieces N and S, or with a plurality of magnetic arms completing the magnetic circuits as shown in Figure 2,, \Ve prefer the latter form because we have found that it gives somewhat superior results, but there is another modification which We have also found to give very nearly as good results, and which has an economical advantage. In this modification, instead of emplo ing a strip form armature, we employ w at we have termed a reed form armature, i. e., an armature which is mounted at one end only, the other end being free to vibrate. Such a construction may be understood from Figure 2 if, for example, the magnetic arms 9 and 10 are eliminated, the voice coil 7a taken away, and the armature 4 cut off, say close to the right hand edge of the pole pieces N and b. The armature will then be in the form of a reed mounted at its left hand end between the magnetic arms 11 and 12. It will be magnetized by the voice coil 8, as has been described, and the operation of this modification will be essentially the same as that which has been described for the other modifications. A return path for each of the magnetic fields produced by the fluctuations of the alternating current will comprise respectively, the armature, the magnetic arm 12, and the pole piece N for one path, and the armature, the magnetic arm 11 and the pole piece S for the other path. There is greater necessity in this modification for careful proportioning of the armature, and it will be advisable to provide an armature, where possible, the natural period of which is outside of the audible range. In speakers of the reed type constructed in this way we have secured very excellent results, and very true reproduction.

We will proceed now to the construction of an exemplary commercial speaker embodying our invention as just described. We have shown in Figure 4 a stamping forming a lamination of our core. For convenience in assembling the motor, as hereinafter to be described, the core is made in two pieces, which are afterward put together to form a completed core. The laminations 18 of Figure 4 are provided with suitable holes and are put together to form the core members 18a of Figures 5 and 6. The laminations may be assembled by means of rivets 19. The front portion N of the core member 18a may conveniently be made a little wider than the rear portion, as shown, and the perforation 14 may be made therein for the passage of the drive rod. The core member may also be provided with erforations 20 and 21 for purposes present to be described. For each motor two 0 these core pieces are employed, onl one of which, however, need have the per oration 14'. In the portion marked N, shoulders 22 are provided to holdithe voice coils.

As shown in Figures 7, 8 and 9, bracket members of non-ma netic material are used and are adapted to attached respectively to the core pieces 18a, and to each other. These brackets may be made of cast aluminum, but other non-magnetic materials will serve. They com rise a bod portion having parts 23 an 24 exten ing at right an les. The part 23 has a flan e portion 25, an the part 24 has another ange portion 26. The flange portion 25 may be provided with perforations 21a whereby it may be fastened to one of the core members. A reinforcing rib structure 27 may join the flan es 25 and 26 across the body of the brac et, and this rib structure may be provided with a boss 28 perforated and threaded as at 29 for the reception of a screw in holding the motor to a suitable support. The flange member 26 has a projection 26a upon one end to hold the armature in the magnetic arms. The flange may have perforations 30 for the rece tion of bolts in assembling the motor. X pair of these brackets is assembled with a core member 18a in such a way thatthe flange 25 is attached by means of rivets 31, passing through the perforations 21a in the flange and 21 in the core member, the portion N extending beyond the bracket, as shown in Fi re 10, and the flange portions 26a exten ing out opposite the portion N and 1 ing in a plane at right angles to the ane of my core piece. The assembly sliown in elevation in Figure 11 may be ground, or otherwise dressed, until the faces of the flanges 26 and the ends of the core piece lie in the same plane. In building up the motor, two of the assemblies shown in Figure 11 are fastened together, with the respective flanges 26 contiguous and parallel, and it will be clear that by introducing spacers between the flanges 26, the core members may be spaced to the extent of producing an air-gap of the desired width.

In Figures 12, 13, and 14, one of the ma netic arm members is shown. It has a boc y portion 32 and flan e portions 33 and 34, one of which is provi ed with notches 35, and the other with an attachment perforation 36.

In utting the motor together, two of the assem lies of Figure 11 are positioned in opposite relationship, as aforesaid. This is illustrated in the side elevation of Figure 24 where the opposed flanges 26 are shown attached together, as by bolts 37 and 38. The extensions 26a are shown in opposed relationship, and between them is the armature 5, and the flanges 34 of arms corresponding to the arms 9 and 10 of Figure 2 and indicated by their body portions 32 and 32a. Where fastened by the bolt 38, the flange portions 26a are spaced apart by three thicknesses of metal, namely, the thickness of the armature and the thickness of the flanges 34 of the magnetic arms lying on either side of the armature. Where the armature passes between the ole pieces N and S of the core structure, tiere will be a space on either side of the armature, determined by the thickness of the flanges 34 between the flanges 26a of the brackets. Thus, b grinding through the faces of the assemblies shown in Figure 11, the pole spacing is secured with a great degree of accuracy by the simple method just described; and a similar spacing is obtained at the rear end of my core structure by inserting between the two parts, the blocks 39 shown in Figures 23 and 25. It is thought that the gen eral assembly of the motor will be clear from a consideration of the several figures.

Figures 19 and 20 illustrate an assembly of the armature 5 and the drive rod 13. The armature has perforations 40 at its ends for the passage of the bolts 38. A field coil structure 6a is shown in the several figures positioned on the rear portion of the core structure. The voice coils are indicated at 7a and 8a, and are illustrated on an enlarged scale in Figures 15 and 16, where it will be seen that in the end flange there is a groove 41. In this construction, the voice coils are held spaced apart by the pole pieces N and S in a horizontal direction, and in order that they may not shift, there is an engagement of the ends of the pole pieces in the notches 41; and the shoulders 22 of the pole pieces engage the flanges of the coils so as to hold them rigidly against motion. This will be clear from a consideration of Figure 23.

Referring again to Figure 2, the voice coils 7a and 8a are positioned very close to the pole pieces N and S, and separated some distance from the point of attachment of the arms 9 to 12 to the ends of the armature. This construction not only facilitates the rigid holding of the voice coils as just described, but it is also advisable from an operating standpoint to prevent the return of flux through the air-gap between the coils and the adjacent arms, whereby the efliciency of the motor mi ht be cut down. To hold the coils against tide pole pieces for this reason, and to secure the positive engagement aforesaid, spring members 42 shown in Figures 17 and 18 are provided, which do not need special description. Their use is illustrated clearly in Figures 21 and 25.

Modifications may be made in our invention without departing from the spirit "thereof, and our invention is not restricted to the specific commercial embodiment herein described.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent, is

1. In a loud speaker motor, members comprising a field assembly providing a magnetic circuit, and an armature member assembly comprising means forming a magnetic circuit, the members forming said circuits lying essentially in different planes.

2. In a loud speaker motor, a field assembly providing a magnetic circuit in which inters aced pole pieces, an armature lying tween said pole pieces, and a saturated magnetic connection between said armature and each of said pole pieces.

3. In a loud speaker motor, a, field assembly comprising interspaced pole pieces, an armature having a central portion located between said pole pieces, a saturated magnetic connection between one end of said armature and one of said pole pieces and a satu rated magnetic connection between the other end of said armature and said other pole piece.

4. n a loud speaker motor, a field assembly having interspaced portions of opposite polarity, an armature of strip form having its central portion located between said field portions, and saturated magnetic arms external of said field structure connecting the ends of said armature to said portions of opposite polarity.

5. In a loud speaker motor, a field assembly comprising interspaced pole pieces of opposite polarity, members providing saturated by-pass paths for a portion of the field flux, said members magnetically connecting said pole pieces at opposite sides, an armature having its central portion located between said pole pieces, said armature magnetically connected to said saturated by-pass members.

6. In a loud speaker motor, a field assembly comprising a magnetic yoke and interspaced pole pieces, an armature having its central portion located between said pole pieces, and magnetic connections between the ends of said armature and said pole pieces, said connections being of a size small enough to be kept substantially in a saturated condition by said field flux.

7. In a loud speaker motor, a field assembly comprising a magnetic yoke and inter spaced pole pieces, an armature of strip form extending between said pole pieces and saturated magnetic connections of strip form between the ends of said armature and said pole pieces, said connections in strip form being magnetically saturated and having less capacity to carry magnetic flux than the component parts of said field assembly.

8. In aloud speaker motor, a field assembly providing a. magnetic circuit and interspaced pole pieces, an armature assembly comprising an armature and saturated magnetic connections between said armature and said pole pieces, whereby a second magnetic circuit is formed in a different plane and coils on said armature at either side of said pole pieces.

9. In a loud speaker motor, a substantially C-shaped field core construction, an armature of strip form extending transversely between the opposed portions of said C,.

saturated magnetic connections between the outer ends of said armature and the opposed portions of said C, voice coils surrounding said armature, and a field coil on a portion of said C.

10. In a loud speaker motor, a substantially C-shaped field core construction, an armature of strip form extending transversely between the opposed portions of said 10 C, ma netic connections between the outer ends OI said armature and the opposed portions of said O, voice coils surrounding said armature, said connections being small enough in area to be kept substantially saturated by the flux in said C.

11. In a loud speaker motor, members comprising a field assembly providing a magnetic circuit, and an armature member providing a magnetic circuit, the members orming said circuits lying essentially in different planes, the armature lying essentially at the center of a balanced magnetic bridge circuit.

12. In a loud speaker motor, a C-shaped field core, a field coil on the back of said core, an armature of strip form transverse to said field core and lying with its central portion between opposed portions of said O, a drive rod attached to said armature and passing through a perforation in one of said opposed portions, and magnetic connections between the ends of said armature and said opposed portions.

13. In a loud speaker motor, a C-shaped field core, a field coil on the back of said core, an armature of strip form transverse to said field core and lying with its central portion between opposed portions of said C, a drive rod attached to said armature and passing through a perforation in one of said opposed portions, and voice coils surrounding said armature and located between said opposed portions and the outer ends of said armature, and magnetic connections between 5 the outer ends of said armature and said opposed portions.

14. In a loud speaker motor, a field assembly comprising interspaced pole pieces, an armature of the reed type having its free end located between said pole pieces, and saturated magnetic connections external of said field assembly between the other end of said armature and each of said pole pieces.

15. In a loud speaker motor, a field as l sembly having interspaced portions of opposite polarity, and an armature of strip form having a portion located between said field portions, and saturated magnetic arms externally of said field structure connecting an end of said armature to said portions of opposite polarity.

THEODORE A. HUNTER. RONALD J. ROCKWVELL. 

